OK, fine then. :-)
Glad that it works (as far as I understand at least).

I'm not going to read the code if you don't have
any issues with it.

0.5% is fairly normal for a (ceramic) resonator.
You need a quartz crystal to get lower errors.

I leave capturing short pulses on a 'scop to others. :-)

Jan-Erik.




Richard R. Pope wrote 2014-07-23 14:02:
> Jan-Erik,
>       The info about crystal frequencies is great. I have a lot of
> crystals from equipment that I have taken a part and it is hard to
> figure out what division to use to get a certain frequency. This will
> make it much easier.
>       Here is the complete code that I am using. I only call the
> InitTimer1() code one time. I call this code in the main() right after I
> have set up the ports and the registers.
>       The chip runs but I can't tell for certain if the code is
> executing. RA0-3 are all high because I have 10k pullups on them. They
> are set up as digital inputs.  I have a 4MHz resonator connected to RA4
> and 5. I am reading 3.979930MHz +- 15Hz. The wave form looks clean and
> steady. I don't care about the 0.5% error at this time.
>       RC0 is floating at about 800 mV. It is set up as an analog input.
> The RC1 bit is high. This is DP1. RC2-5 are low and this is correct
> until RC4 and 5 are pulsed high. RC2 and 3 are DP2 and 3 and they are low=
..
>       The pulse on RC 4 is only for one second. This is the gating pulse.
> The pulse on RC5 is only for a few uSs. This is the clear display pulse.
> I have never learned how to set up my scope to capture a very short
> pulse. Could you please tell me how to do that? I have a Tek 465B.
> Thanks,
> rich!
>
> //    Includes go here
> #include <pic16f684.h>
>
> //    Prototypes go here
> void main(void);
> void delay(int time);
> void resettimer(void);
> void InitTimer1();
> //void Interrupt1();
>
> /*Richard R. Pope
>    07-19-14
>    */
>
> #pragma config FOSC =3D XT, WDTE =3D OFF, PWRTE =3D ON, MCLRE =3D OFF \
>           CP =3D OFF, CPD =3D OFF, BOREN =3D OFF, IESO =3D OFF, FCMEN =3D=
 OFF
>
> // Crystal Freq =3D 4MHz
>
> // Global variables
> int count =3D 0; // number of interrupts counter
>
> void main(void)
> {
>
>       PORTA =3D 0b00000000;        //    Turn porta off
>       TRISA =3D 0b11111111;        //    Set Porta as all inputs
>       PORTC =3D 0b00000010;        //    Set RC1 to high
>       TRISC =3D 0b11000001;        //    Start with DP1 on, the rest of
> portc is inputs
>       CMCON0 =3D 7;         //  Turn off Comparators
>       ANSEL =3D 16;         //  Set RC0/AN4 as analog
>       InitTimer1();        //    Set up the timer
>
> // Define commands
>       int    DP =3D 1;            // The decimal points are counted from =
1
>       int Reset =3D 33 + DP;    // Turn on RC5
>       int GateOn =3D 1 + DP;    // Turn on RC4
>       int GateOff =3D DP;        // Leave only the DP on
>       int    GateTime =3D 1;        // The count time =3D 1 Second
>       int    DisplayTime =3D 15;    // The display time =3D 15 seconds
>
> while (1 =3D=3D 1)            //    Loop forever
>       {
>           PORTC =3D Reset;        //    Clear the Display
>           PORTC =3D GateOn;        //    Start counting
>           delay(GateTime);            // Count the frequency for one
> second =3D HZ
>           PORTC =3D GateOff;
>           delay(DisplayTime);            // Display the frequency for 15
> seconds
>
>       }
> }    //  End NewControlCode.c
>
> void delay(int time)
> {
>       int limit =3D time * 10 + 1;
>
>       TMR1ON =3D 0;        // Turn the timer off
>       TMR1IE     =3D 0;    // Disable timer interrupts
>       resettimer();    // Reset the timer to starting values
>       count =3D 0;        // Reset the timer interrupt counter
>       TMR1IE     =3D 1;    // Enable the timer interrupts
>       TMR1ON =3D 1;        // Turn the timer on
>
>       while(count < limit)
>       {
>       }
>      return;
> }
>
> void resettimer(void)
> {
>       TMR1H =3D 0x3c;    // Reset the timer to roll over
>       TMR1L =3D 0xb0;   // at 100mS
> }
> //Timer1
> //Prescaler 1:8; TMR1 Preload =3D 3036; Actual Interrupt Time : 100 ms
>
> //Place/Copy this part in declaration section
>
> void InitTimer1(){
>     T1CON                 =3D 0x31;
>     TMR1IF     =3D 0;
>     resettimer();
>     TMR1IE             =3D 1;
>     INTCON             =3D 0xC0;
> }
>
> void Interrupt(){
>     if (TMR1IF){
>       TMR1IF =3D 0;
>       TMR1H     =3D 0x3c;
>       TMR1L    =3D 0xb0;
>       count++;
>     }
> }
>
> On 7/23/2014 6:11 AM, Jan-Erik Soderholm wrote:
>> Yes, this is not a major issue for code that is, let's
>> say as an example, in the startup coe that only is run
>> one at each power on anyway. Code readability and
>> clarity is far mor importent in that case.
>>
>>    > It also sounds like the compiler will actually generate
>>    > better code if I use the whole register.
>>
>> Yes, that will always be s simple 8 bit "load".
>> Three instruction maximum (bank switch, MOVLW and MOVWF).
>> Four on the (old) 684, the bankswitch takes two. :-)
>>
>>    > I prefer binary over either hexadecimal or decimal
>>    > for setting the bits on a port.
>>
>> Right, for registers that hold a "value" (such as an timer
>> register for example) the format (hex/bin/dec) is of less
>> importance. Many times a decimal value can make the code
>> easier to read such as when setting a timer to "one hundred
>> and twenty three". Decimal (123) is easier to read then
>> hex (7B).
>>
>> For registers where the individual bits has different functions
>> (such as INTCON or similar) I prefer binary. That makes it
>> easier to read out the bit settings.
>>
>>    > Why is there a setting for the starting point of the counter in
>>    > both the Interrupt handler function and in the InitTimer function?
>>
>> I do not have the code in front of me, but I'd expect anything
>> with "init" in its name to only run once at startup.
>>
>> So InitTimer run once at power on and setup the basic timer stuff.
>> The ISR then sets whatever has to be set at each interrupt, such
>> as reloading the timer value (if not freerunning).
>>
>> B.t.w, *if* one can find a setup where you get a usable "timing"
>> while letting the timer fre-run (that is, without ever re-loading
>> the timer value), it is often easier to get a consistent overall
>> timing in the application without having to bother about specific
>> adjustments for some extra instructions here and there. This can
>> sometimes need a carefull selection of the crystal frequency. And
>> that is also why there are all those "odd" crystal values... :-)
>>
>> Here is a good overview of crystal frequencies:
>> http://en.wikipedia.org/wiki/Crystal_oscillator_frequencies
>>
>>
>> Jan-Erik.
>>
>>
>
--=20
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